This invention relates to an improvement of a filter element adapted to be incorporated into filtering devices such as an air cleaner, oil filter or fuel filter used, for example, in an internal-combustion engine.
A conventional filter element for such filtering devices typically comprises a pair of end plates having central apertures and a filter material such as paper having rough surface. A long strip of the filter material is reversely folded to form a series of sections or pleats of uniform length to thereby increase the filtering surface, and the material thus folded is secured between the end plates to define a cylindrical shape having a central passage for the filtrate. Such typical filter element is ilustrated in FIG. 1. The pleats are indicated by reference numeral 1 and are connected to each other at outer ridges 2 and at inner ridges 3 which defines an outer circumference 4 having a radius D1 and an inner circumference 5 having a radius D2, respectively.
Performance of the filter element of this kind is mainly determined by total volume of the filtering surface. The filtering surface can be increased or enlarged either by increasing the dimension of each pleat 1 or by increasing the number of the pleats. The enlarged dimension of the pleat is obtained by increasing the radius Dl and/or decreasing the radius D2, but the filtering devices usually limit the size of filter element. On the other hand, by increasing arrangement density the number of the pleats per unit of voulme can be increased to the extent that the two adjacent pleats can be separated from each other sufficiently to permit the fluid to flow therebetween and to minimize the loss of capacity due to the accumulation of dust, sludge and the like.
In the conventional element as illustrated in FIG. 1, the pleats 1 are arranged generally radially and are symmetrical with respect to the center of the cylinder. Therefore, the distance A2 between the adjacent inner ridges 3 is smaller than the distance Al between the adjacent outer ridges 2. In other words, the density of the pleats 1 thus arranged is increased toward the inner circumference 5 and reduced toward the outer circumference 4. Consequently, even if the pleats 1 are so arranged as to have a density of maximum permissible value at around the inner circumference 5, there are necessarily created extra and vain spaces at around the outer circumference 4. This limits the efficiency of the filter element of the prior art.
It is therefore an object of the present invention to provide a filter element having an improved efficiency and capacity.
Another object of the invention is to provide a filter element in which density of the pleats can be increased with maintaining intervals between the pleats sufficient to permit the fluid to flow therebetween.
A further object of the invention is to provide a filter element in which the number of the pleats can be increased to thereby enlarge the filtering surface.